Osteosynthesis plates for implantation, anatomical reduction and internal splinting of bone fragments after fractures are widely known. A bone plate for osteosynthesis could be of a general type, which means that the bone plate is not adapted to a certain anatomical position, or it might be of a specific type, which means that the properties of the bone plate have been adapted in order to correspond to a specific type of an anatomical position. For the elbow or distal humerus, the following various solutions have been offered to date (cf. FIGS. 1 to 5):
1) System comprising different plates for an osteosynthesis of a type which is not anatomically specific. These plates were produced for arbitrary anatomical circumstances and may therefore also fit on the distal humerus. These bone plates must be shaped during the operation in order to be adapted to the anatomy of their final anatomical destination, in this case to the shape of the distal humerus;
2) Systems of two osteosynthesis plates cooperating on one bone, one of the plates, the medial or the lateral one, having been anatomically pre-shaped in order to fit the medial or the lateral column of the distal humerus. The other plate is of a type which is not anatomically specific and has to be shaped during the operation in order to fit in its position in the distal humerus;
3) Two-plate systems, one of the plates being pre-shaped in order to fit the anatomy of the lateral arch of the distal humerus, and the other plate being pre-shaped in order to fit the medial ridge of the distal humerus, in positions virtually parallel to one another. These plates require no deformations or only a few deformation during the operation. Bone screws which are introduced through one of the plates come into contact at an obtuse angle with the bone screws which were introduced through the other plate, which is referred to as so-called distal locking of the screws;
4) Two-bone plate systems, one of the bone plates being pre-shaped in order to fit the anatomy of the dorsal aspect of the lateral part, and the other bone plate being pre-shaped in order to fit the medial ridge of the distal humerus and the two plates being fixed on the humerus in positions almost perpendicular to one another. These plates require no deformation or limited deformations during the operation. Bone screws which are introduced through one of the plates come into contact at an acute angle with the bone screws which were introduced through the other plate; and
5) Two-bone plate systems as under 4) above, but, in addition, the plate extends not only distally but also laterally in the most remote distal region of the lateral osteosynthesis plate, said plate having a hole there. Through this hole, a bone screw will come into contact with the bone screws which arrive from the medial plate, at an obtuse angle.
In contrast to other methods, such as simply encasing in plaster, screwing with bone screws or bandaging with wires, osteosynthesis plates have the advantage of fixing a plurality of bone fragments and attaching them in a stable manner to the healthy tissue. In principle, all considerations in the production of osteosynthesis plates were based on the object of forming the shape of these osteosynthesis plates for the implantation on the bone so that anatomically correct positioning and fixing of the osteosynthesis plate without the necessity of changes on the bone and with substantial protection of soft tissue are achieved. The osteosynthesis plates therefore should not be bulky and should have various possibilities for fixing (a plurality of drilled holes).
With the systems obtainable on the market, there are the following disadvantages:
1) Non-specific pre-shaping of the plates requires complicated bending of the plates, which may lead to a loss of mechanical stability of the plate osteosynthesis. Complicated adaptation of the plates is moreover time-consuming. Since the plates are not optimized for the distal humerus, lack of bone support and fixing points for the bone screws may result;
2) For stability reasons, a two-plate system was and is preferred for the distal humerus. With a plate which is shaped to fit a specific anatomical point, and a plate which requires adaptation to its position, the advantage of a system comprising two specially pre-shaped plates is, however, not achieved.
3) A disadvantage of a plate system having a parallel plate configuration is that it requires that all bone fragments lie approximately in a planar, relatively flat space between the two osteosynthesis plates or can be contacted there by inserted bone screws. If, however, bone fragments lie slightly outside this relatively narrow, planar space, they cannot be contacted by the known osteosynthesis plates or by the bone screws in the known osteosynthesis plates and held with reduction. Moreover, the inventors observed that the one-row osteosynthesis plate may have only very little stability to tilting out of the connecting axial plane of the holes. Accordingly, the possibility of loading the bone provided with the plate may therefore be greatly limited.
4) A right-angled plate arrangement ensures stability to tilting but lacks the possibility for screw engagement at an obtuse angle between the bone screw which was introduced through the lateral plate and between the bone screws which were introduced through the medial plate. For very distally located fractures and for fractures in osteoporotic bone, the lack of the meeting of the screw directions at an obtuse angle, the so-called lack of amalgamation via the distal block, will reduce the retention of the bone plates in the bone and hence the stability of the osteosynthesis.
5) A combination of the right-angled plate configuration and a lateral plate form which permits an acute-angled screw engagement between the lateral bone screw which was introduced through the plate and the medial bone screws which were introduced through the plate is ideal for the stability and the retention, but the anatomy of the distal humerus must be followed. The distal part of the plate which is laterally extended must not disturb the soft tissue and the function of the elbow. Systems which are on the market and correspond to this description may disadvantageously come to rest in the region of the points of action of the tendons and thus possibly disturb the function of the elbow. Moreover, the known plates for osteosynthesis do not permit sufficient fixing by the distal block on the medial side.
It is therefore an object of the invention to improve the known sets so that the osteosynthesis plates firstly have better retention on the bone and secondly a larger number of different bone fragments can be reliably repositioned relative to one another. This should take place in a manner which protects soft tissue.